CRSI |
ENGINEERING
DATA REPORT NUMBER 34 |
ASTM A706 REINFORCING BARS TECHNICAL INFORMATION WITH COMMENTARY ON
USAGE AND AVAILABILITY |
 A
SERVICE OF THE CONCRETE REINFORCING STEEL INSTITUTE
933 N. Plum Grove Rd., Schaumburg, Illinois 60173-4758 |
INTRODUCTION
The types of reinforcing bars used in the United States are
billet-steel, rail-steel, axle-steel, and low-alloy steel. Billet-steel bars, conforming
to the ASTM A6151 specification, are the most widely used type. Low-alloy steel bars, conforming
to the ASTM A7062 specification, are the most recent type."
Questions are frequently raised by Architects/Engineers and
Constructors regarding A706 reinforcing bars. Their questions typically are concerned with
a wide range of practical items such as mechanical properties, weldability, availability,
and relative costs.
This report has resulted essentially from the dialogue with many
Architects-Engineers and Constructors. The major requirements in the ASTM A706
specification are discussed in a question-and-answer format. Information on the usage and
availability of low-alloy reinforcing bars is also presented.
DEVELOPMENT OF SPECIFICATION
Q1: When
was the ASTM A 706 specification issued?
A: The first edition of the specification was adopted in 1974.
Q2: Why was the specification prepared and Q2: adopted as an ASTM standard?
A: The report by ACI Committee 4393 includes an interesting description of the background and
development of the ASTM A706 specification. The Structural Engineers Association of
California (SEAOC) was influential in getting ASTM to prepare and issue the A706
specification. In seismic design, it is essential for the reinforcing steel to have
controlled tensile properties. SEAOC wanted a reinforcing bar specification that would
have the necessary controls on tensile properties, and include requirements to enhance
ductility and bendability. To facilitate construction, SEAOC also wanted the specification
to provide for weldable bars.
Q3: Are there any other points regarding the background or development of the
specification that ought to be mentioned?
A: From an historical perspective, perhaps it should be mentioned that during the
period when SEAOC was pressing for a new specification, there was also considerable
activity in nuclear power plant construction in the USA. The Joint ACI-ASCE Committee 359
on Concrete Components for Nuclear Reactors also had an interest in development of the new
specification.
It should also be noted for the record that a major producer of
reinforcing bars at that time (1960s) made a proprietary deformed bar that had essentially
the desired mechanical properties and requirements for weldability. The rebar producer
provided considerable input to the A706 specification.
MECHANICAL PROPERTIES
Q4: What
are the main requirements for tensile properties in the A 706 specification?
A: The specification covers only one strength level of bars, that is, Grade 60;
hence the specification prescribes a minimum yield strength of 60,000 psi. The prescribed
minimum tensile strength is 80,000 psi. There are also two other limits (controls) on
(tensile) strength properties; the yield strength cannot exceed 78,000 psi; and the
tensile strength cannot be less than 1.25 times the actual yield strength.
The latter requirement, a minimum tensile-yield ratio, will control
when the actual yield strength of a bar is greater than 64,000 psi (the yield strength
obtained in a laboratory tensile test). In other words, if bars were tensile-tested in a
laboratory and the measured yield strengths, in psi, ranged from 64,000 (plus) to 78,000,
the corresponding tensile strengths would have to range from at least 80,000 (plus) to
97,500 psi. As an example, suppose the laboratory measured value of yield strength was
68,000 psi; to conform to the specification, the measured tensile strength would have to
be at least 1.25 x 68,000 or 85,000 psi.
Q5: What other tensile properties are prescribed in A706?
A: Percentage of elongation; the A706 specification requires larger values of
minimum percentage of elongation as compared to the values prescribed in the other
specifications for reinforcing bars.
Q6: What other mechanical properties are prescribed in the specification?
A: Similar to the other rebar specifications, A706 requires bend tests. The bend
test requirements are more restrictive (smaller bend test pin diameters) than those in the
other specifications. See Reinforcing Bar Testing4 for the bend test pin diameter
requirements in the reinforcing bar specifications.
© Copyright 1990 by the Concrete Reinforcing Steel Institute
